1. Field of the Invention
The present invention relates to a non-vulcanized, kneaded rubber designed for expandable formulation uses. More specifically, the invention relates to a kneaded rubber suitable for die forming sponge parts, principally comprising continuous foam, to be used, for example, for producing door roof weather strips.
The kneaded rubber material for expandable formulation, according to the present invention, is applicable not only as die forming and sponge rubber material, but also as an extrusion molding material and a material for producing foam rubber products principally comprising closed-cell foam.
2. Description of the Related Art
A door weather strip will now be taken as an example for purposes of explanation. Sealability and a soft touch when opening and closing are demanded for door weather strips and the like. Therefore, at least the part of the strip facing the door should be formed of a sponge rubber with a low rebound elasticity.
The main parts of weather strips are extrusion molded, while the corner and end parts thereof are die formed using injection and transfer molding techniques. The sponge rubber comprises a low-viscosity blend, that is highly fluid at high temperatures so that the rubber can retain fluidity in dies for die forming and injection fluidity for injection molding.
Meanwhile, kneaded rubbers for expandable formulation, as prepared with kneaders such as the Banbury mixer and kneading rollers, are at a relatively low viscosity. These rubbers are generally stored so that the rubbers are folded together in a form of continuous sheet or continuous tape. Therefore, the rubbers are adhesive with a small kneaded rubber viscosity (green strength).
The following problems occur regarding the handling of the resulting kneaded rubbers after termination of the kneading procedures:
(1) After the termination of the kneading procedures, the resulting kneaded rubbers readily adhere to and remain on kneading rollers, involving a large variation in the material weight per unit area, when the kneaded rubbers are cut out in a sheet shape or in a tape shape from the kneading rollers. The kneaded rubbers readily remain on the rotors of the Banbury mixer, and thereby contaminate a subsequent batch with extraneous materials.
(2) Adhesion preventives, such as talc and surfactants do not function satisfactorily to permit storing the resulting kneaded rubbers in a folded shape. Therefore, these rubbers should be immersed in a water tank for storage. More specifically, a large volume of adhesion preventives causes die contamination (in both transfer and injection molding) and thus induces potential connection failure between the die-formed part and the main extrusion formed part of weather strip. Furthermore, kneaded rubbers storage in water, absorb water, leading to a frequent incidence of variation in the expansion ratio.
(3) Materials designed for single transfer molding, so-called ball materials, adhere together, leading to frequent occurrence of variation in the ball material weight when the ball materials are prepared by cutting.
(4) Due to the low green strength, the rubbers cannot be fed sufficiently into the feed rollers of material loaders, such as injection molding machines or extruders, so that molding failures readily occur due to poor loading of the materials.